ALBUQUERQUE, N.M. (AP) — A watchdog group has filed suit to halt a multibillion-dollar plutonium factory proposed at Los Alamos National Laboratory.

The Los Alamos Study Group claims the Chemical and Metallurgy Research Replacement building is meant only to increase the production capacity for the cores of nuclear weapons, known as pits.

The lawsuit, filed Monday in federal court in Albuquerque, alleges the U.S. Department of Energy and the National Nuclear Security Administration have violated the National Environmental Protection Act by preparing to build the project without an environmental impact statement.

The two agencies and their top administrators are named as defendants.